In general, rubbery latex is used in preparation of impact-resistant resin compositions for improving impact strength thereof. An agglomerating agent is used for preparing the rubbery latex. Various methods for agglomerating rubbery latices have been employed up to now.
For example, in preparation of ABS resin which is impact-resistant, the resin is prepared by agglomerating polybutadiene rubber particles with an agglomerating agent, graft-polymerizing monomers of styrene and acrylonitrile onto the polybutadiene latex, and mixing the grafted polymer and SAN (styrene-acrylonitrile) copolymer.
In an impact-resistant resin, particle sizes of rubbery latex affects impact-strength of a molded article of the resin, as well as other physical properties thereof.
Generally, it is preferable that the particle sizes of the rubbery latex are in the range of 0.25.about.1.0 .mu.m. For preparing the rubbery latex having particle sizes of 0.25.about.1.0 .mu.m, there have been various researches on agglomerating agents, methods for preparing the agents, and methods for agglomerating rubbery latices.
Japanese Patent Publication No. 56-45921 discloses a method for increasing particle size of synthetic rubbery latex using a latex that is polymerized from 97.about.70% by weight of an alkyl acrylate of C.sub.1 .about.C.sub.12 and 3.about.30% by weight of an unsaturated acid in the presence of an anionic surfactant.
Japanese Patent Laid-open No. 58-61102 discloses a latex as agglomerating agent which is prepared by emulsion-polymerization of an unsaturated acid, an alkyl acrylate, and monomers polymerizable therewith, and a method for preparing the latex.
Japanese Patent Publication No. 1-32842 discloses a latex as agglomerating agent which is prepared by emulsion-polymerization of an unsaturated acid, diene monomers, and monomers polymerizable therewith, and a method for preparing the latex.
U.S. Pat. No. 3,049,500 teaches a method of increasing the size of the polymer particles in a synthetic rubber latex of a copolymer of butadiene-1,3 and styrene which comprises incorporating in the latex of polyvinyl methyl ether and an alkali salt electrolyte.
U.S. Pat. No. 3,330,795 teaches a latex consisting essentially of a mixture of a synthetic rubber dispersion and an oxidized polyalkylene oxide having a molecular weight within the range from 3,000 to 30,000 and a substantial --C.dbd.O group content of not more than 8%.
U.S. Pat. No. 3,403,125 discloses a method for agglomerating a rubber latex using an agglomerating agent obtained by reacting a polyoxyethylene glycol with the diepoxide obtained by condensing epichlorohydrin with a polyhydric (alcohol) phenol.
European Publication No. 0029613 A1 discloses an agglomerating latex containing (1) a polymer selected from (a) homopolymers of alkyl acrylates and methacrylates in which the alkyl has from 1 to 12 carbon atoms, and (b) copolymers of ethylenically unsaturated monomers capable of forming water insoluble homopolymers, and (2) a non-ionic surfactant consisting of an addition product of ethylene oxide.
European Publication No. 0143858 A1 discloses an agglomerating agent copolymer having an elastomeric "core" and grafted thereto a "shell" of interpolymer comprising polymerized acid and ester comonomers.
European Publication No. 0406806 A2 discloses an agglomerated rubber copolymer prepared by emulsion-polymerizing an alkyl acrylate/1,3-butadiene mixture, and then agglomerating the resulting rubbery copolymer. The agglomeration is effected by adding (a) an acid group-containing copolymer prepared by emulsion polymerizing an alkyl methacrylate/unsaturated monomer mixture, and (b) an oxy acid salt selected from alkali metal, alkaline earth metal, zinc, nickel, and aluminum salts of oxy acids.
When an alkyl acrylate is used as an agglomerating agent of a rubber latex, a semi-batch type is employed due to a severely exothermic reaction of the alkyl acrylate. This process has an advantage in removal of exothermic heat. However, the process does not form uniform cores, and provides latex particles having a large distribution of particle size.
When an ionic comonomer is used in the preparation of an agglomerating agent for agglomerating rubber latex, the ionic comonomer should exist at the surface of the agglomerating agent to be prepared, thus having a high agglomeration effect. According to conventional methods for preparing an agglomerating agent, the ionic comonomer exists inside the agglomerating agent, but not at the surface of the agent.
The present inventors developed an agglomerating agent which can effectively agglomerate rubber latex by reducing reaction times of agglomeration.
U.S. Pat. No. 5,294,659 teaches a method for emulsion polymerization of butadiene in an emulsion polymerization medium, comprising providing an emulsion polymerization medium containing monomer consisting essentially of butadiene and up to about 50% by weight of an aryl olefin comonomer, and a soap, and adding an acrylic latex to the emulsion polymerization medium during the polymerization.
Korean Patent Publication No. 94-10341 teaches a method for preparing rubber latex having increased particle sizes by adding 0.1.about.10 parts by weight of a latex for controlling particle size, comprising diene monomers and aqueous monomers capable of agglomerating polymers, at the time of polymerization conversion rate of 80%. And, Korean Patent Publication No. 96-854 discloses a method for preparing a latex having an increased particle size, a high solids content and a high glass transition temperature, comprising reacting an aryl olefin compound or alkyl methacrylate compound with/without a vinyl cyanide compound in the presence of an emulsion polymerization medium, and adding 0.1.about.10 parts by weight of a controlling agent of particle size to the emulsion polymerization medium when the polymerization conversion rate reaches to 5.about.50%.
Considering the reaction temperature and solids content of a rubber latex, conventional methods cannot produce rubber latex having an increased particle size. Particularly, when a certain solids content of rubber latex is to obtain, the reaction times are long, which is uneconomical in the production of rubber latex.
In accordance with the present invention, the inventors provide methods for preparing rubber latex having an increased particle size at a certain reaction temperature and solids content, and for reducing reaction times, thereby improving productivity of rubber latex.